[xy] Some improvements on multi project

[wangxiaoyou1993]

Description

• Remove unnecessary project model initialization
• Check user project setting with env var instead of sub project's project setting. Env var is ENABLE_USER_PROJECTS
• Remove duplicate feature flag check

How Has This Been Tested?

• Tested locally

Checklist

• The PR is tagged with proper labels (bug, enhancement, feature, documentation)
• I have performed a self-review of my own code
• I have added unit tests that prove my fix is effective or that my feature works
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

cc: